How the Glaciers at Glacier Bay National Park Were Formed

Glacier Bay National Park contains the most rapidly moving glaciers known by scientists.
©2006 National Park Services
Great chunks of ice break away from the
face of an advancing glacier and collapse
into the water with explosive force.
The process, known as calving, is one
of the park's most stunning sights.

The 16 glaciers that wind their way down the valleys of Glacier Bay National Park like tremendous white highways were formed during climatic periods when more snow fell during the winter than melted and evaporated in summer.

As snow builds up in layers winter after winter, its own vastly increasing weight causes the snow to compact into small grainy pellets that become crystals of ice. Eventually, this level of ice reaches such a great depth and weight that it begins to move downhill in the direction that is dictated by gravity.

The compacted ice crystals deep beneath the surface function like frozen ball bearings, gliding over one another and enabling the entire mass of ice to slide. As one of these glaciers inches its way into the waters of Glacier Bay, fissures that have developed in the ice along with the rough motion of the sea causes huge chunks to break away, or calve, with a resounding crack that can be heard miles and miles away.

Glacial Retreat

In 1794, when British sea captain George Vancouver sailed up the Alaska coast, Glacier Bay did not exist. Vancouver saw only a great wall of ice, several miles wide and thousands of feet thick, where the bay now lies. In the intervening two centuries, the ice receded more than 65 miles, leaving in its wake a spectacular fjord-rimmed bay, surrounded by forested mountains that only now are returning to life following a long hibernation.

At the southern end of the bay, where the ice first departed, the land is now covered with a lush rain forest of spruce and hemlock. Looking today as though it had been there forever, the forest of great trees, rising from a spongy moss floor, has been able to sustain rampant growth because of moisture-bearing winds from the Pacific that supply year-round precipitation. Farther north, in areas of the bay more recently deglaciated, the vegetation is sparser and the terrain more rugged.

Glacier Bay National Park is one of the few accessible places that icea calving can be seen.
©2006 National Park Services
The glaciers are pulling back from the land at a rate of about 1.5 feet per year.

At its head, the bay branches into two great arms, Muir Inlet and West Arm. They in turn are feathered by numerous small inlets. Alder and willow forests today grow on slopes that were covered by glaciers only 50 years ago. But at the heads of the small inlets, glaciers calve icebergs, which drop into the water with the roar of distant cannon. This sound is called "white thunder" by the Tlingit Indians.

There are 16 tidewater glaciers that flow down from the mountains to the sea at Glacier Bay. Most of the glaciers in the park's eastern and southwestern ends are receding at rapid rates, but some glaciers on the west side are advancing. Scientists believe the depth of the water in the inlets, which affects air temperature, plays the crucial role in determining whether a glacier retreats or advances.

When the sun breaks through the clouds, the icebergs scattered throughout the park are struck with light. It truly is an awesome sight. For hundreds of thousands of visitors each year, Glacier Bay is a place of pure epiphany and revelation.